Why do we use outtake fans? Doesn't a PSU take out the hot air of the case?!..

[Dance123]

Hi,

Why do we all use outtake fans. If I am right most PSU's have a fan at the bottom that takes in air and a fan at the back where the air can go out the case. Isn't that actually enough? It's just something I was wondering. There must be a logic answer to this. Anyone?

I am no expert, but why do PSUs have an intake (mostly at the bottom side) and outtake fan since I suppose there task isn't to take out hot air like an outtake fan does. Makes me think that there must be lot of dust inside a PSU after a while, not? Why do they design PSU's that way?

 

[sniperruff]

well the PSU fan is not gonna suck enough air by itself

if you buy a case like dell's where they have the air scope, an 80mm fan connecting to it would be enough cool a stock P4

 

[lazybum131]

Most common PSU's have two fans, but you don't actually need two fans for the PSU.
Any of the real quiet PSU's use only one fan (if not fanless).

If your case uses positive pressure (intakes sucking in more then exhaust blowing out) then you don't necessarily need to use more exhaust fans then the PSU one.
But the same goes for negative pressure (exhaust blowing out more then intakes), you don't necessarily need the intakes either.

In terms of having JUST a single fan (PSU) taking out all the hot air but also not having positive pressure, it might not be a good idea with modern computers (high-end CPUs and videocards, not to mention overclocking and overvolting). The airflow from the power supply fans aren't that great, if you open the PSU up you'll see that airflow is pretty restrictive in there.

 

[Baronz]

Originally posted by: lazybum131
Most common PSU's have two fans, but you don't actually need two fans for the PSU.
Any of the real quiet PSU's use only one fan (if not fanless).

If your case uses positive pressure (intakes sucking in more then exhaust blowing out) then you don't necessarily need to use more exhaust fans then the PSU one.
But the same goes for negative pressure (exhaust blowing out more then intakes), you don't necessarily need the intakes either.

In terms of having JUST a single fan (PSU) taking out all the hot air but also not having positive pressure, it might not be a good idea with modern computers (high-end CPUs and videocards, not to mention overclocking and overvolting). The airflow from the power supply fans aren't that great, if you open the PSU up you'll see that airflow is pretty restrictive in there.

One PSU outtake and no intakes works for me, although it does get a bit hot, it's worth it to have a quieter computer. But it's definatly doable, you just need to have the right cooling for your stuff.

 

[MDE]

Most PSUs can barely exhaust their own heat with the fans inside, let alone the heat from the rest of the system. If you're really worried about noise throw a Panaflo or Vantec Stealth in there. Slow fans are better than no fans...

 

[sniperruff]

like i said, get a case that takes a 120mm and it'll be almost silent.

 

[Czar]

Originally posted by: sniperruff
like i said, get a case that takes a 120mm and it'll be almost silent.

yeah, and change it to 5v instead of 12v, then its silent

 

[Xtremist]

I don't have anything really to back this up, but I'd be curious if the more you equal out the intake and outtake flows with fans, the better. Obviously for airflow it would be, but it'd also be interesting to know if "generally" two fans working at a real high efficiency would produce less sound than one fan working less efficient.

Honestly I'm just throwing this out. I can't really see that it'd be MORE quiet, but I do wonder if it would make only perhaps 1.4-1.5X the noise as a single fan..

 

[sniperruff]

i just think that putting more outtake fans is better than putting more intakes.

the position of the outtake sucking out would create a current right on top of the CPU (that is, if the case is nicely designed). the outtake fans are designed to suck air so air would go on top of the HSF

intake fan on the other hand, i really don't see the point. the only advantage i can think of is cooling the HD if you can mount one right in front of the HD cage.

other than that, an intake fan just make more noise

and i think since most case fans does not change speed... i would doubt that putting 2 would be quieter than putting one. IMO it would make more noise, but the cooling aspect would be much better

all these silent talk make me want to throw out my old antec and get a new sonata...

 

[Dolemite76]

more outtake airflow than intake will suck out more heat. it creates less pressure inside the case thus forcing air from the outside to enter the case from any open area on the case whether you have intake fans or not. if you want a quieter system. don't use any intake fans, use one or two outtake fans (quiet fan models work great here) in addition to your power supply outtake. if you want better airflow at the cost of more noise, use at least one intake fan with two or more outtake fans plus your powersupply fan (if you have the space on your case). you can also stack outtake fans on top of each other to increase airflow, it won't double the airflow, but it will increase it nicely at the cost of even more noise. if you want a setup like this i really have to recommend using quiet case fans. Antech and Thermaltake provide great solutions. hope this helps.

 

[Xtremist]

sniperruff - See, I just don't see that... There has to be as much air going out of the case as is coming in. I suppose it's possible that with a single fan (or multiple's that don't pull evenly) the air inside the case might be slightly compressed and so less would be entering/exiting initially, but once it's going it would have to suck in as much as it blows out, regardless if the fan is place in the front or back? Otherwise your case would just end up exploding at some point due to the constantly increasing air pressure inside the case I really don't know, but that sounds right... right?

Granted, placing the fan (if only one) closer to target hot spots like the CPU could help more due to the fact that the air may be moving more rapidly in a more concentrated area near the fan, helping cool the CPU down better than if it was mounted up front.

I'm still not sure you're right about the multi-fan noise issue. It seems to me there are two factors that produce the sound due to fan usage. First, the actual air moving and being sucked/expelled. Also the actual movement of the fan mechanically. I would think if you had a fan that had to not only pull air into the system, but also in a way push the air OUT of a system it would tax the fan more. It may be able to keep up a constant RPM, but it's not working very efficiently. If it had a matching fan that was taking up half the workload for it, could the mechanical noise from the fan be less? I don't quite know, but I do think there are various things that work better/quieter when they don't have to work as hard to do their job (like me!) I agree it'd make more noise overall, but I don't think it'd be exactly twice as much noise as just the single fan. Oh well, doesn't matter a whole lot anyway really..

Dolemite76 - That doesn't make sense. Perhaps for the first few seconds it'd work, but after the system is running and the airflow is established you aren't going to continually have more outgoing airflow than incoming. If that was the case, at some point your case would become a vaccume and implode. It may produce a lower pressure initially. I'm curious what really would happen if a case were made to constantly output more air than it intakes. Eventually you'd have removed all the air in the case it seems... Anyway interesting stuff. If I get really bored, you've inspired me to try a few experiments out Thanks!

 

[AgaBoogaBoo]

Dance123: People who do have more fans than the basic PSU fan(s), are people from three categories, for the most part: 1. Overclocks 2. People who want the piece of mind the system will stay cool 3. People who need it due to components

My current setup, P4 2.8C GHz, Radeon 9800, 512MB Corsair XMS, and 120GB WD 8mb Cache is using a PSU with one fan and a 120mm outtake fan. I added the outtake because I didn't want to rely on the signle fan PSU to keep the system cool. In my older P4 1.7 GHz system, I added a single panflo fan only when I added a second hard drive.

Most systems don't really need an outtake fan for the average user who has a single HD and doesn't OC.

The PSU's second fan is to help cool it, obviously, but it also helps in cooling the case, possibly eliminating the need for an outtake case fan, then again, that fan is probably added since the PSU gets hot.

 

[JustAnAverageGuy]

Keeping mind that the case would have to AIRTIGHT for more outtake than intake fans thing to work.

And at some point, the fan would be overwhelmed with the air pressure. The air pressure outside would eventually push in, even if the fan was blowing out. It can only blow out so hard, and air pressure would eventually win.

 

[AgaBoogaBoo]

Originally posted by: JustAnAverageGuy
Keeping mind that the case would have to AIRTIGHT for more outtake than intake fans thing to work.

And at some point, the fan would be overwhelmed with the air pressure. The air pressure outside would eventually push in, even if the fan was blowing out. It can only blow out so hard, and air pressure would eventually win.

Dude, we're like... dealing with little computer fans, not some air conditioning unit. The chance of having a pressure problem would take quite some time. Even if it was airtight, and you had more outtake and intake, the outtake would cause the intake fans to spin faster... thats all...

 

[sniperruff]

xtremist: i think if all the fans are on the back, then air would just try to get it whereever possible, aka the front vent, the gap between the cd-rom... so they basically try to suck air from wherever possible and try to lead air right above the CPU

well at least AMD recommends that exhaust fans to be used, and stated that intake fans are useless in their system builder guide. i forgot the link nor have a copy but i remember it when i was building my computer last year

and what do you people mean the case is air tight. we all have vents (big ones in my antec) in the front!

oh extremist... no the case would not blow up. sucking more air out in the back would cause more air to be pulled from the front, WITHOUT any fans. however this may result in a dirty case since air is being sucked from the front, literally from every little gap

but i have a fan mounted in the front HD cage, and air is stilled being sucked from every tiny gap!

 

[sunase]

>but once it's going it would have to suck in as much as it blows out, regardless if the fan is place in the front or back?

I played around a lot with my system when I was first putting it together and positive pressure (more intake fans) definitely gave me hotter running components than negative pressure (more outtake fans). You want the hot air by the big heat producing components drawn out as fast as possible and fresh air getting pulled in from all the cracks/grates/vents in the case - not the other way around with hot air potentially getting pushed past your hard drives and chipset on the way out and whatnot.

 

[JustAnAverageGuy]

I was assuming you were talking about a tower with absolutely no vents, gaps, holes of any kind, and only one fan as the only possible entrance exit of air for it.

 

[0roo0roo]

i'm sure way back in the day it was enough, but now we're using 350+watt psu's and extreme heat output cpu's/gpu's. a few cfm's from a psu isn't enough, esp when it has to fight the pressure alone.

 

[Gerbil333]

My Enermax 460W PSU's fans are so quiet and slow that I wouldnt know they were on if I didnt see them spinning. I can hardly even feel any air being moved. I use Enermax PSU's in all my systems. Other power supplies seem to use louder, faster fans, but those still push very little air.

Computers generate a lot of heat, and there's no way the PSU's fan(s) could take care of it. I try to get enough exhaust in my case to make air circulate around all the components (click sig for pics of my case). My third computer only has the two Enermax PSU fans and the CPU's hsf. It works great. In fact, we had a party here in the room it was in last night. It became the stereo and people were dancing in there, so the room temp got pretty hot. It did fine. I actually have some high speed 120mm and 92mm fans on there, but they're hooked up to a rheobus and I have them turned off. When I turn them on, that adds about 160-180cfm of airflow and is capable of dropping the CPU temp by about 10C. I built that rhebus and added those fans to the side panel when the case contained a different system. The current nForce 2 IGP board doesn't need it though. The northbridge is even passivelly cooled.

 

[Xtremist]

JustAnAverageGuy - Thanks, that's exactly what I'm saying There's no way a case could blow out more air than it takes in or vice-versa. At least not without doing something very bad at some point

AgaBooga - I think the point both myself and JustAnAverageGuy are trying to make is that you CAN'T have a setup that blows out more than it sucks in or sucks in more than it blows out. At least not practically. Yeah, if you had two out fans and only a single intake and the entire case was airtight besides the fan areas, the intake would be forced to spin faster by the desire to equal the pressure.

sniperruff - Right That's what I'm saying You simply can't have more output or intake than the other, it will all be equal no matter how many fans you have. Unless it's a sealed system besides the intake or outtake. Then it would just stop to pull/push once the pressure got so high/low (I still like to think it'd end up blowing up or imploding!).

Nono, I'm not saying any computer cases are air tight. I was responding to statements that you should have more outtake air than intake. That's not possible UNLESS your system is air tight besides the outtake vent.

oh extremist... no the case would not blow up. sucking more air out in the back would cause more air to be pulled from the front, WITHOUT any fans. however this may result in a dirty case since air is being sucked from the front, literally from every little gap

LOL, I'm not saying it really would man. Again, I'm simply trying to point out that you cannot have more outgoing or (in the blow up case) incoming air than you have incoming or outgoing (respectively). IF you did, it'll blow up... Again, not seriously, but for some reason the scene of that happening in my head is quite amusing for whatever reason

Yikes, I think I've been misunderstood. That happens quite a bit, especially when I don't explain myself very well and expect others to know my thoughts. Go figure We generally agree, the whole thing about things blowing up was to illustrate you can't have more going in one direction than another. The case will get it from somewhere.

Now I remember why I don't post much. Hopefully some of you had fun imagining your cases blowing up at least

 

[jiffylube1024]

Originally posted by: JustAnAverageGuy
I was assuming you were talking about a tower with absolutely no vents, gaps, holes of any kind, and only one fan as the only possible entrance exit of air for it.

Even this is pretty much an impossibility. Most cases have some form of front vents (thank god) and no case is airtight. Air will get in there somehow, and a huge buildup of pressure is not a concern. Your case is not going to explode from too many case fans, trust me on this one .

 

[thaotherweirdkid]

Originally posted by: Xtremist
sniperruff - See, I just don't see that... There has to be as much air going out of the case as is coming in. I suppose it's possible that with a single fan (or multiple's that don't pull evenly) the air inside the case might be slightly compressed and so less would be entering/exiting initially, but once it's going it would have to suck in as much as it blows out, regardless if the fan is place in the front or back? Otherwise your case would just end up exploding at some point due to the constantly increasing air pressure inside the case I really don't know, but that sounds right... right?

Granted, placing the fan (if only one) closer to target hot spots like the CPU could help more due to the fact that the air may be moving more rapidly in a more concentrated area near the fan, helping cool the CPU down better than if it was mounted up front.

I'm still not sure you're right about the multi-fan noise issue. It seems to me there are two factors that produce the sound due to fan usage. First, the actual air moving and being sucked/expelled. Also the actual movement of the fan mechanically. I would think if you had a fan that had to not only pull air into the system, but also in a way push the air OUT of a system it would tax the fan more. It may be able to keep up a constant RPM, but it's not working very efficiently. If it had a matching fan that was taking up half the workload for it, could the mechanical noise from the fan be less? I don't quite know, but I do think there are various things that work better/quieter when they don't have to work as hard to do their job (like me!) I agree it'd make more noise overall, but I don't think it'd be exactly twice as much noise as just the single fan. Oh well, doesn't matter a whole lot anyway really..

Dolemite76 - That doesn't make sense. Perhaps for the first few seconds it'd work, but after the system is running and the airflow is established you aren't going to continually have more outgoing airflow than incoming. If that was the case, at some point your case would become a vaccume and implode. It may produce a lower pressure initially. I'm curious what really would happen if a case were made to constantly output more air than it intakes. Eventually you'd have removed all the air in the case it seems... Anyway interesting stuff. If I get really bored, you've inspired me to try a few experiments out Thanks!

haha, nice...there are imploding and exploding cases out there now? for either thing to happen you would need an airtight case, not too many of those floating around...otherwise air will vent where it needs to and attempt to reach equilibrium, even if the only place it can leak is back through the fan, which is what would happen before imploding or exploding, the fan would not beable to create the kind of pressure required for that...

thaotherweirdkid

 

[sharkeeper]

First of all, it's known as exhaust fan, discharge fan, NOT outtake fan!

If you have fans removing air from your case, it does help to have fans drawing air in to help reduce negative pressure and excessive amounts of dust getting drawn in around openings, apertures, chassis junctions, etc.

For every 100 liters/minute of air removed from the case, you should have about 110 liters/minute of make up air being drawn in the case. Make up fans should be filtered as well. If the particulate count is high with smaller sized contaminates, you should consider using more aggressive filter media and/or treatment to increase contactor efficiency. It is very important to remember that a more efficient filter also has a much higher resistance to airflow so a 50 liter/min (free air) rated fan is really pulling 30 liters/min (or less) when the filter carts are in place. If the makeup falls too far behind the (theoretical) air being removed, the internal pressure drops and the exhaust fan efficiency plummets. Dusts will begin to invade the chassis as well.

The efficiency of your case ventilation can be demonstrated easily with the use of smoke. You will know immediately if it obeys the guidelines as outlined above.

Why bother? With today's high powered peripherals, a hot spot in the case that goes unseen can easily be the cause of instability or premature failure. Good engineering will result in a case that runs very cool AND is quiet.

Cheers!